Re: [PATCH] queue stall with blk-mq-sched

[Hannes Reinecke <hare@suse.de>]

On 01/26/2017 05:42 PM, Jens Axboe wrote:
> On 01/26/2017 09:35 AM, Hannes Reinecke wrote:
>> On 01/25/2017 11:27 PM, Jens Axboe wrote:
[ .. ]
>>> And another variant, this one should be better in that it should result
>>> in less queue runs and get better merging. Hope it works with your
>>> stalls as well.
>>>
>>>
>>
>> Looking good; queue stalls are gone, and performance is okay-ish.
>> I'm getting 84k IOPs now, which is not bad.
> 
> Is that a tested-by?
> 
Not yet; while doing the performance analysis the system now got a queue
stalled with _legacy_ SQ.
Need to figure out if it's my mpt3sas patches or something else.

>> But we absolutely need to work on I/O merging; with CFQ I'm seeing
>> requests having about double the size of those done by mq-deadline.
>> (Bit unfair, I know :-)
>>
>> I'll be having some more data in time for LSF/MM.
> 
> I agree, looking at the performance delta, it's all about merging. It's
> fairly easy to observe with mq-deadline, as merging rates drop
> proportionally to the number of queues configured. But even with 1 queue
> with scsi-mq, we're still seeing lower merging rates than !mq +
> deadline, for instance.
> 
> I'll look at the merging case, it should not be that hard to bring at
> least the single queue case to parity with !mq. I'm actually surprised
> it isn't already.
> 
Thanks.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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